How do I start Notepad++ from cmd?

Even though the Notepad++ directory is not in your path, you can use the command below to run the program from the command prompt:

start notepad++

To open a file in Notepad++, run:

start notepad++ <filename>

You could add C:\Program Files (x86)\Notepad++ to your PATH environment variable.

For example, you could run the following on the command prompt:

set PATH=%PATH%;C:\Program Files (x86)\Notepad++

For further options, see What are PATH and other environment variables, and how can I set or use them?

I would not want to clutter my PATH just for using a single tool.

One alternative is to use an alternative text editor as 100% replacement for Notepad as explained here with many details. Another description with a dedicated editor launcher tool can be found here. Another Notepad++ launcher on github.

A less invasive alternative is a cmd file like this:

"C:\Programme\Notepad++\notepad++.exe" %*

This file has to reside somewhere along the existing PATH. I actually put all my tools in one common UTIL directory, which is part of PATH.